The use of hydrogen gas (H2) fueled fuel cells such as polymer electrolyte membrane fuel cells (PEMFCs) offer the potential of reducing carbon dioxide (CO2) and eliminating nitric oxide emissions from vehicles. However, current technology does not offer economically attractive options for storage of enough hydrogen gas to deliver the driving range to which motorists are accustomed. Instead of carrying a tank of hydrogen gas, vehicles could carry a tank of liquid fuel such as an alcohol. The alcohol, typically methanol, would pass through a fuel processor that converts the methanol to hydrogen gas that immediately passes to the fuel cell. In this fashion, hydrogen-powered vehicles need not carry any hydrogen tanks.
The process for converting methanol to hydrogen is known as “steam reforming” and is described by the following (unbalanced) chemical equation:CH3OH+H2O═CO+CO2+H2To operate efficiently, the steam reforming reaction must be run in the presence of a catalyst. It has been reported by Isawa et al. that Pd/ZnO is a highly selective catalyst for steam reforming of methanol. See Catal. Lett. 19, 211-216 (1993).
For the purpose of developing an efficient fuel processor, weight and size of the energy device are major considerations. In order to reduce overall size of the on-board power system, insulating material should be minimized. This requires that steam reformer to be operated at relatively low temperature.